Define "long enough."
I still have around three inches of exposed skin when I roll a Magnum XL all the way on, but I figger the chances of that part of my penis ever penetrating anything are fairly remote anyway. If nothing else, the ring on the end of the condom gives a good visual reference when you're trying to gauge how deep you can thrust without boxing her cervix into oblivion.
So, it's not long enough to cover all of me, but it's long enough for any reasonable expectations.